If it helps, think of the water first like a perfect mirror. If it’s a perfectly flat mirror then it would look like there’s another duck upside down below this duck. If you want to be extra precise, it’s mirrored across the plane where the duck meets the water.

But water isn’t usually perfectly flat mirror, and here you have little nods to there being ripples or waves. The choppier the wave, the less it reflects, so you’ll often see people break up the mirrored reflection at the choppiest parts of the wave. Similarly, waves aren’t flat, depending on the part of the wave/ripple you’re at, you’d be reflecting higher or lower as though the mirror is tilted to the angle of the surface.

The last tricky part is that most surfaces are more reflective at a glancing angle than head on, so often reflections are stronger further in the distance and closer up you’ll just be looking down into the water. On a more technical note, you can look up the index of refraction to learn more about this phenomenon.

To tie it all together, this is why those long shots of sunsets have a sun reflection that is really long (much longer than the size of the sun in the distance) - because it’s at a distance it’s a strong reflection and because all the waves are reflecting at different angles you’re getting all the glancing reflections of the sun on the top of each wave. It typically being dark at sunset also means the bright sun reflection blooms to make it look brighter and larger than just the tip of the wave.

Conversely, in water sports like wakeboarding, you might not see much of a reflection at all because all the water is choppy and non-reflective.

Looking down into a pond, you might not see a reflection either because the angle is too steep to reflect.

In short, yes, in this case the reflection should probably be roughly the same size.

I think so, but my optics courses date back to a long time ago...

It will look really nice on stickers!