The common inside DS transducer used by several instrument sellers is from AirMar, and is designed to adjust to most angles, and then seal up OK with a sound-transfer fluid like antifreeze inside it.
Over the years I have had two of these. One that fell apart due to poor design of the plastic housing, and about 15 years later another one that seems to be working fine to provide a signal to our Lowrance plotter.
Note that the steepest dead-rise will be for installations in the bow sections (duh) but while 'tradition' prefers that location there is really no reason not to put your "puck" transducer further aft. Only caveat is not to put it too close to the keel root as the transmitted 'cone' of sound should have a clear shot downwards.
On our prior boat I put an inside DS transducer under the cockpit where the bottom was fairly flat. Present boat has its inside transducer under the front part of the cockpit.
Purists will tell you that moving it aft, while solving installation problems, will give you less warning when approaching shallow waters. If you do the math for how many feet the boat moves forward at, say, 5 kts... the difference in potential warning is maybe one or two seconds. Maybe less.
i.e. no real-world difference, IMHO.
If you are planning to install it thru the hull, you still have to deal with the same forward dead-rise angle problem.