Why is uncapping done *after* training?

[#1]

Hi folks,
Being a keen geek, I recently spotted that my exchange had finally been 21CN'd, so raised a ticket with PN to be switched to ADSL2+
That was carried out earlier this week and I've gone from ~8Mbps ATM sync to ~10.5Mbps sync.
That's all great but what I really want is faster upload. Being stuck at 440Kbps is no fun.
Thanks to this forum I discovered that PN keep a cap of 440kbps on 21CN connections, so have asked for that to be removed. I've been told, though, that this can only take place after the 10 day training period.
What I don't quite understand is why...
1) The training period doesn't really do much other than allow BT to set a minimum speed threshold, such that in future they can investigate issues if your speed drops significantly below this.
2) PN claim the reason they cap uploads is due to it possbly causing instability if run at full rate. OK, I don't personally see the logic but if those are the rules then fair enough.
So... Putting 1 and 2 together, how can it be sensible to let a line "train" and set it's operating parameters and *then* change the way it operates by removing the cap?... It just doesn't make sense to me.
Personally I just want 1Mbps upload ASAP. I had it at my old house (O2 LLU) on a line with far worse characteristics... no capping, no faffing, it just worked.
Anyone know why PN insist on waiting to remove the cap?
Cheers,
Bobsta

[#2]

Quote

Anyone know why PN insist on waiting to remove the cap?

AFAIK Its probably just that BT's systems won't accept any orders during the training period.
If the original order for the move to 21CN was placed with an upload cap ( which is usual ) then BT won't accept an order to uncap the upload until after the training period has completed.

[#3]

An Engineers reply:
You only change one thing at a time. Then you can eliminate what is causing the problem far easier.
Here we have 3 issues
change from 20CN to 21CN
ADSL1 on 21CN or ADSL2+ on 21CN
upcapping the upload.
So you swap the line to ADSL2+ on 21CN and see if there are any problems.
If there are (the higher frequencies may indeed cause some on a few lines) you then re-provision on ADSl1 on 21CN.
Once you have confirmed that all is OK on ADSL2+ on 21CN only THEN you upcap the upload and re-check all is stable.
If you do all three at once you have no idea where to start if there suddenly start to be instabilites etc on the line.
Additionally I suspect of all the customers Plusnet have (? a few 100 thousand?) the ones that want the increased upload are actually a small minority.
So they BT/Plusnet set up the system to cater for the majority at least cost and rectification work for themselves and provide a fix for the minority (uncap upload at a later date).

[#4]

Quote

You only change one thing at a time. Then you can eliminate what is causing the problem far easier.

That's definitely the closest answer, BT's systems don't block us from placing an order, however we do prefer that any additional changes to the circuit are done after training so that it makes other potential issues easier to identify.