Work out the odds of actually getting three flesh wound. You need to hit the target, then roll a 1/6 on the ammo dice to get the three shots then roll a 4+ to inflict a flesh wound three times.

It actually occuring to that degree is rare.

First of all, low probability of a highroll does not cancel out the fact that you can highroll and completely remove a model no matter the save or remaining wounds (or completely cripple that model).

Secondly, when using rad-phage you mostly care about getting the effect

*at least once, *which actually has a very good propability,

65% of that happenning.

The link is anydice script I've done for calculating probability of wounding by rapid fire weaponry, in this case its the same probability as getting at least 1 wound of no save T3 target by S3 rapid fire. (Be warned if you decude to use the script for other purposes though, I've also included traits like shock and shred and these are not working correctly currently.)

So no, rad-phage per every hit would be ABSOLUTE BONKERS. GW clearly wrote it so it triggers at the end of attack sequence and only once, no matter how many times you hit.