Hi Michael,
Thou all you said was correct, I 100% agree that It is makes the transmission very complecated but improving the SNR or to change the data rate in the channel would mean redesigning the whole system all over again, and making packet size shorter in first place would mean wasting resources if in case the data size is say 40k., (each time I have to send all headers and trailers for every frame i transmit)
so in dynamic resizing scheme all i did was to send 1k data at once if any error occured I send 1k/10, and so on. thus saving a some time.