How to increase the distance of wireless power transfer?
Beyond a certain distance magnetic flux density reduces with the cube of distance. To avoid this you need bigger diameter coils. Try googling for the formula because unfortunately I'm on an android and haven't learnt to embed pictures using one.

Something also to consider is making a passive coil extender if this is practical for your application. Basically it's two sets of coils that take power at the drive end and deliver it to the receiving end.

Lowering inductance will cause a higher coil current and this delivers more flux at a greater distance for a certain drive voltage but you will need to consider litz wire to make this effective. Basically you need to maintain Q at lower inductance values.