The simple answer is ‘it depends’, as there are many factors that will affect your stroke’s forward reach, including shoulder mobility, stability, strength, core control and cadence.
A common refrain from coaches is to stretch forward in your stroke, to reach for more water. But by doing this, more stress, pressure and demands are placed on your shoulder. As a result, you can end up ‘gliding’, i.e. losing momentum, slowing down and forcing you to work harder.
So we need to keep the arms always moving – not necessarily at the same speed all the way around, but certainly not stopping. When your arm travels forward on entry, aim downwards slightly into the water and extend – but not to a full stretch. Depending on your shoulder mobility, you may have to go lower in the water, but this is fine. Basically, you want to be in the best position to bend your elbow and get your forearm/hand pointing straight downwards. Once you’re in this position you can accelerate your hand and arm backward and reach as far back as possible.
Shortening your stroke very slightly at the front end might feel like you’re not putting down as much power – you’re not, and your cadence will come up. But you won’t need to work as hard to generate forward movement, so your effective stroke length will actually go up.