I have always found the issue of higher angle firing in the period to be interesting. As a former user of heavy weapons, I can comment from personal observation on the amount of force generated by firing, and that most of the means to absorb the equal and opposite reaction employed today did not exist then - hydraulics and recoilless for example. For field guns the recoil was accepted by the carriage and dissipated through the rearward movement of carriage, so design of the trail and the axle was important in order to accept the stress while minimizing the extent of recoil. An angle of fire above the horizontal would cause a portion of the recoil force to be directed downwards applying significant stress to the axles and wheels. I would expect that the material employed in carriage construction would have a physical limit as to how much downward vector could be accepted before failure. The only pieces capable of firing at a significant angle were mortars, which generally fired from a solid bed.
I would be interested to learn the maximum angle that field pieces (both guns and howitzers) could accept before damage was probable. I suspect that that angle was greater than the maximum angle found in firing tables of the day. How did this change over time, and where do the licornes fit into that data?
I would also be interested to know about the endurance of mortar beds. Given the rather massive calibres I have seen in museums, I wonder at the possible charges and ranges. If the charges were significant, then I am curious about the absorption of the downward vector, and whether the rearward vector was an issue. The force exerted by modern mortars on their base plates is substantial and for best effect they should be staked in. I could see a period mortar bouncing significantly when fired unless secured. Since mortars were mostly used in sieges, were the firing emplacements constructed specifically to retain the mortar beds? Is it fair to say that mortars were not suitable for field use due to the time required to prepare a suitable firing point, and the immobility of the piece once emplaced?