I think the lighter a boom is, the more sensitive to length it is. The more boom you keep in, the less side to side movement you will get in it, more overlap between sections. It also helps the boom deflection, the more overlap the sections have, making it less "whippy". The National we have now is not real happy out at the full 95', its much better behaved at 85-90'.
Our Rt is similar- it has 110' main, and setting trusses its better behaved at 100-105'.
I don't have this problem in my tms 300, if I put it all out, main at 105' or with jib at 136', I'll just run it there for the whole job (trusses/ cycle work). I don't think I ever run it with a little telescoped back in. Same with my 25 ton groves. If I put jib in at 106' I can set trusses there until I have to telescope in a little to set the close ones. But those booms are really rigid, and that's the difference. And they are fairly slow on the boom, so it doesn't tend to get away from you booming down. More stick out, speeds it all up when your changing a lot of radius (setting trusses), and they are slow enough to begin with, the extra length just helps.
My 70 ton would be a great crane if you only ever ran it on main boom. If you put all the jib in and dead stick out, (188') its just too fast to be smooth and easy. It runs best with either just jib and no dead stick out (130-160 depending if you have the stinger out on the jib) or just dead stick (127'). The power pin/ dead stick gives a lot of deflection with the jib installed. It actually acts better with just jib on with no power pin, (100' main + 30' jib) than it does with power pin out on main (127'). The jib is more rigid than the power pin section.
If I'm setting heavy stuff with my 70, 35, or Rt, I like to run out only what I need for boom, the charts are better, and every hydraulic input movement, means less movement at the boom tip. Its so much easier to be precise the slower that everything happens.
If you really get into reading charts and studying them, there's quite often instances where more boom gets you more chart at radius, and some cranes have a "super strong" place. Some cranes with say 150' of main may have a 111' boom chart that is 1,000lbs better than any other boom length chart. I've been studying a lot of all terrain charts recently, and I notice it in them.
Link belt uses a A mode and B mode on some of their truck cranes. A mode in those, gets you a much better heavy picking chart, by only extending the bigger section of boom. 35' - 60' of boom out. It makes a big difference in their up close lifting charts. B mode is for the longer boom lengths.
The Grove tms 870 I used to run had a A and B mode too, but the A mode in it, sent out the lighter sections, only helping if you were running without counterweights. Any counterweight installed, B mode was always better charts in the grove. I always had counterweight on, so the only time I used A mode was if I needed all the boom out, it was faster to telescope it all out in that mode. Other than that, A mode was useless.
