Combining Rigid Phenolic Insulation & Fibreglass in attic - Virtues of same?

Folks,

Began insulating my attic space yesterday & while the rafters are deep enough to accomodate 125mm kingspan & still retain a 50mm ventilation path, the truss tye (horizontal section of the truss) will only accomodate 80mm kingspan (phenolic boards). I cannot squeeze 125mm into it as there is 4 x 1 bracing running across all the tye sections. I was therefore going to fit the 80mm between the tyes & run 200mm fibreglass over the tyes in the void above, & composite plasterboard on the underside of the truss. Is there any value to be gained by using a combination of the two (rigid phenolic & fibreglass) to increase the amount of insulation fitted? I know one option may be to run the rigid boards all the way up the rafters to the to the ridge, but with the positioning of the bracing & tyes, it would be a right pain & wouldn't necessarily lend itself to a good snug fit in any event as it gets very awkward in the confined space. As I type this I'm wondering also, is there any value in fitting the 80mm tight between the tyes & laying loose rigid boards directly on top of these in the void, thus increasing the thichness??? Thanks in advance, boots