I thought that's what it must be, it's just that
For a 90 end feed elbow (15mm) inpact is 10mm per elbow - is obviously Too Much
For a 90 compression (22mm) impact is 11mm per elbow - is obviously Too Little
For a 90 solder ring (15mm) impact is 15mm per elbow - obviously Depends on the fitting!
Oh never mind!