I understand why it would be great to have overlapping sample decays.
However with quad engine, 4 mini engines x 2 voices (for unison / stereo samples) = 8 voices. Overlap is simply not possible because it would introduce inconsistent behaviour in voice stealing between mini engines / pulses.
If you want overlapping sample playback I would suggest using subtractive, setting source B to sample, and then setting the envelopes for the synth oscillators to 0ms so that you only hear the sample.