I have recently bought a Sankey electric propagator & I have noticed that
In my heated greenhouse which runs at approximately 62F the soil
temperature
in the Sankey can rise to nearly 95F.

I bought a Sankey just over a year ago and had exactly the same problem.
Mine held two standard seed trays and was rated at 22 watts - ie 1 unit of
electricity (Kwh) per 45 hours, or 5 pence per day.

I raised the same point on this forum. On reflection, I think it was a
false economy to buy one without a thermostat. There is a heated mat built
into the bottom, which, without a thermostat, constantly consumes 22 watts.
This will raises the temperature, say, about 30 degrees above ambient. If
ambient in your greenhouse is -30F, the pad will raise it to 0F inside the
propagator. If the ambient is 100F, it will raise it to 130F inside. So
the temperature you get depends on the ambient.

I also bought a small propagating thermometer. I found (as you would
expect - on reflection) a big temperature gradient from the bottom of a pot
to the top. The heating mat itself might be running at 120F, an inch above
it the soil might be 100F and another inch above the soil might be only 80F.
You will get a temperature gradient like this in any propagator as the soil
is a poor conductor of heat. I put mine on a sheet of polystyrene, so as
not to lose heat downwards, this just makes it hotter above. Even a small
amount of ventilation will change the temperature. The net result is that
you are not in control of this and most other propagators. And if you are
measuring the temperature on the surface, your plant roots could be 20F
hotter.

Solution. I bought a freestanding thermostat, which cost more that the
propagator - but then as a physicist I like to be in control. Otherwise 1)
reduce the ambient temperature of your greenhouse, or 2) put an inch or two
of sand in the base, with your pots on top. This lifts your plants farther
from the heating element, and 3) open the ventilator.