Would epicenters in less-deep areas of ocean tend to reduce the impact of a resulting tsunami somehow (wave "breaks" before getting there?)
Tsunamis are created when large volumes of water are displaced vertically.

The predominant ways this can happen are when an earthquake of significant magnitude is created at a subduction zone - one tectonic plate subducting under another tectonic plate. During such an event, part of one plate moves downwards or upwards very quickly causing the water above it to be displaced vertically.

The other predominant way a tsunami can occur (seismically) is when an earthquake causes massive subsidence or slumping of material on the ocean floor - such as an underwater landslide. This can also create a significant vertical displacement of water. It is speculated this was the cause of the October 2018 tsunami in Palu, Indonesia.

There are meteorological causes of tsunamis but I won't address them because your question relates to seismically induced tsunamis.

The epicenter of an earthquake, whether under shallow or deep water, is largely immaterial to the creation of tsunamis. What is is critical is whether the earthquake has caused sufficient water to be displaced vertically either through sea floor movements (tectonic plates) or slumping or subsidence of sea floor material.

The difference between a quake under shallow and deep waters would be the size of the tsunami - how much water has been displaced vertically, how much energy has been imparted into the water and thus how high any wave will be and the destructive energy that it has.

Humans have tried to create tsunamis but were largely unsuccessful. During World War II, in Project Seal, New Zealand tried experimenting with explosives in what is now Shakespear Regional Park. Likewise, the US did similar experiments during nuclear weapons testing in the Pacific Ocean - Operations Crossroads and Hardtack, at Bikini Atoll. The heat from the nuclear weapons produced a lot of steam, but not significant tsunamis.