I don't know about disa, but what tubes are you talking about? M42 inj aren't air shrouded... so what tubes?
intake tubes the whole intake is a little bigger. Before i running plastic DISA i broke them into peaces 6 times

and all the plastic pieces stucks in my sparks

each time cost me a brandnew DISA and 4 spark plugs

now im running metal DISA from m42 with a capasitor 62ohms in the valve cable it works perfect!
Impedance and flow I'm sure at 100%.. can't remember the exact numbers because I'm not at home now, but they are exactly same impedance and same flow. I had them connected and the m44 ecu gave not a error;)
soo... the problem is my injectors condition