Not sure Blu-Tac will have much effect on BL5s! 😂

I would suggest damping the room a bit when you do the test sequence. More furniture, maybe rugs if you don't have carpet down and some more bodies in the room. Then remove said bodies etc and see what it sounds like. Probably take some trial and error to get them as you wish. Try moving the speakers away from the walls a bit more as well.  

You'll find great variations in where the bass impacts depending upon placement and listening position.

B&O's claim that these speakers will adapt perfectly to any room and can be positioned anywhere is a bit of a stretch. I get great differences if I place them in different places. 

Here's an image showing how energy dissipates in a room 5.3x3.6m from a woofer (here placed in the middle of the room, but don't bother with that) - it just shows you how you'll have peaks and valleys with more or less bass in different positions in the room (height, width, length coordinates).

 Here's a quick snapshot from my listening room. I've tried the speakers in the corners, at a position just in front of the edges of the cabinet, and where they are now (and a lot of places in between.)
For accurate listening, with a natural bass rendition, where they are now is best. The calibration buttons are 1.77m from the back wall and 1.08m from the side walls. When I had them about 80cm farther back, there was imprecise bass in my listening position - but lots of bass about 60 cm in front of it. My head, when listening now, is 2.9m from the central column of each speaker.

So - first set them up where you'd like to have them, but have a chair and move that about until you find a good bass. See if that's where you'd like to have your listening position. If not, then you're probably going to have to move the speakers about and have the listening position fixed.

Yes - your room could be soft, or the cavity underneath could be swallowing the bass. You could always set up your speakers in a larger room, and then move them into the one you're intending them for, in case you're very bass hungry. But I've found them to be able to accommodate well to a variety of room configurations, if natural bass rendition is the goal. And in spite of the room calibration evening things out somewhat compared to the illustration above, you will still have to contend with and accommodate how the sound waves are propagating in the room.
 

B&O's claim that these speakers will adapt perfectly to any room and can be positioned anywhere.

Forget it!

In some cases the callibration doesn't goes well,to much bass.

I'm wondering if b&o will come with better callibration software for difficult houses.

I can't understand why they didn't make a manual fine tune button for the low frequencie at the back side of the loudspeaker.

I don't know whether they've ever said it will adapt perfectly to any room, but they have said you have great freedom of placement. Which is true if you're not aiming for critical stereo perspective - but if you are, then you should follow traditional rules of placement. And there  will always be room shapes/materials that any kind of bass-calibration on this level couldn't do anything with.

I remember you've had some challenges with your speakers, which you felt gave too much bass. That's a problem I've never encountered, though I have tried them in a variety of different rooms. 

I'm in the process of installing an ARC software solution in my listening room, which will control the entire frequency range of all audio output to my speakers when listening in stereo.

link

One would need this program, plus a DAW (digital audio workstation) program. You then measure your room and have the program recalibrate the output to fit a target frequency distribution. Sounds complicated and isn't, once set up the processing will be handled by my Mac mini. B&O should offer it as built-in, in their BeoCenter 2 Audio and the coming BeoSound 5, to show they are serious about perfect sound. (There are various surround sound receivers that have such Audyssey room calibration incorporated.)

I'd advice both the thread starter and Koenig to look into those possibilities, you end up with fantastic sound even in problem rooms.

I don't understand it,

How do you connect this to the beolab and beosound?

The signal that comes out of your BeoSound has to be passed through the software, before being sent on to the speakers.

As I'm not using a BeoSound, but playing from a harddisk, I can do the processing in the computer before sending the processed signal to the speakers.

But in your case I would consider using this:

The issue will be the meter or so gap between the speakers. Instead of the bass firing down onto a solid floor which will help reduce unnecessary vibrations/reinforce bass reproduction, the sound will be traveling into what is essentially a giant box (boxes + bass = disaster) - kinda like placing a subwoofer on top of a large wooden box (it's going to sound sloppy, slow and 'empty).

Short of reinforcing the floor with concrete blocks or filling in the gap with concrete or generally making the floor more rigid, you won't be able to do too much.

That doesn't mean the issue doesn't lie somewhere else though. High ceilings and a lack of soft furnishings will really make things worse.