Voretex
First, you need to find out why there is a belief that more CAS is needed. This is one potential solution to the issue. What could well be needed is some form of kinetic effect that could come from a variety of means - hence joint fires. CAS is but one element.
It is not that the RAF can't push any more ac out there, as far as I can tell none have been requested. So has the Land Chain of command got it so wrong? So, second, you will need to identify why the joint commander hasn't requested any more CAS assets. This could be for a variety of reasons.
One could be (and this is a big could) that there is a blance required for everything. We all know that our LoCs are extremely taut; therefore, it is unlikely that there will be any spare capacity to support extra assets (of whatever hue) in theatre. The 'So What?' is if the Jt Commander needs some more assets he has to lose something elsewhere to compensate. Ergo more CAS means less infantry/RE/Medical/Arty/Avn/Armour/ISTAR (delete as appropriate). It's a tough call; but, this is why CJO is a 3* (currently infantry). He is best place to decide the best force laydown - If he wants more CAS we'll be ready to supply it.