sagging floor insulation?

jpc

Hello everyone, gotta quick question about my previously installed insulation, Pulled the ply decking up on the attic side of my kneewall above garage in order to install rigid foam blocking in the joist bays directly underneath kneewall., but a handfull of the bays I can see the insulation sagging away from the top of the cavity, in the bays where the fit is right and its up tight agianst the underside of the upstairs floor there is about six inches between the bottom of the insulation and the back side of the garage sealing, so took a quick look around house for something I could maybe slide in there and try to work the sagging insulation back up into place but no luck, but even if I did find something to work, what would I used to insure it stays there after I block the bay up and call it done, being the garage walls and ceiling is already drywalled and my only access is in the kneewall area on both side, does anybody have any suggestions,tips or input on this.If drywall removal is the only solution it would definitly have to be a tax time job due to financial's. I appreciate everyone's time,thank you