Why does a BD35F work at all RPM settings yet has a fixed length cap tube.

After installing a new fridge system the option was available to run the compressor at 2000 RPM up 3500 RPM but what revs should be chosen to match the cap tube. After reading Henry Ehrens excellent cap tube article it would appear that only one setting would work but they all work, this should not be possible.

So noting the discharge and suction pressure, amps draw and cycle time for various RPM settings with no other changes, the system was run at many RPMs and the following table is a synopsis of many tests and it does appear that 2500 revs is the most thermally efficient. Of course pull down from warm is quicker at higher revs but so is the power consumption!

Revs
On time
cycle time
amps
A/hr
3500
10
13
6.2
4.77
3000
6
9
5.9
3.93
2500
5.5
8.5
4.6
2.98
2000
8.5
11.5
3.7
2.73


The discharge pressure changed by only 2 PSI between any test and the suction stayed about the same. It certainly does not fit with any cap tube sizing data one can get so anyone with an idea why this setup is so forgiving?

Bestest Chef