If you use tensol 30 or the like , you can flood the flat piece with solvent and just place the other piece atop it , the exposed areas flash off on and only at the acrylic to acrylic contact point will any melt occer. This is a very poor way to bond stuff as the bond strength is very weak. You should chamfer the edge and use a fill type glue to fill in the "wedge". the problem , as I explained is not air bubbles per se , it is the edge finish whose microgrooves can not be filled with a material that has the same refractive index thus making the bond invisible , any high points on the edge will give a really bad bond and dips or low points wont bond at all if you use high flash point solvents. Its better to disolve a small amount of acrylic in the solvent and use this as it slows evaporation and acts as a fill as well as giving the glue a slight increase in viscosity.When we bond stuff this way we fill a syringe and needle with the solvent and run it along the seam between the piece and the flat surface whilst pressing the piece down and capilliary action fills the join. When glueing larger areas to others , it's best to apply glue to the underside of the top piece in a X fashion with a bit of an extra blob in the middle of the X . As you press down air flows out the top and sides of the X and you get a bubble free join, You can laminte large surfaces together with an almost optically clear join this way , the key is the air escape path.
