Help me understand PDC related to buffer size

So... i have set my buffer to 128 samples.
I insert a plugin that reports 4 samples of PDC.
Reaper reports 128 samples of PDC on that track.
I insert another instance of that plugin. That means 8ms in total.
Reaper reports 256 samples of PDC.

SO how come? I should only have 4 samples of latency on the first instance, but OK, i guess the engine can only work in multiples of the soundcard buffer, and it starts a 128 sample chunk.
Now what i don't get, is if i add another 4ms, it begins a totally new chunk and i get 256 PDC.
That's insane for only 8ms!!!

This way i get insane latencies all the time if i stack just a few plugins together with minimal latencies.

Is this the only way this can work? Are other DAWS handle this better?

THanks

Help me understand PDC related to buffer size