I think most people find the bike-to-run transition quite difficult while the legs adjust from going in a circular motion to running. Particularly for longer distance courses.
Here's an interesting article from a renowned triathlon athlete/coach:
The article discusses the merits of putting your cleat towards the rear of your foot / under the arch vs the more traditional ball-of-foot location. Having re-located the cleat to the arch of his foot, Joe (the author) found that his performance improved.
Moving the cleat towards the rear of the foot engages the larger quads and glutes muscles, taking the strain off the calf and leaving you fresher for the run.
So perhaps you should give it a whirl? The article references a Speedplay adaptor that enables this cleat position, though I haven't seen it myself. As comments underneath the article identify, there may be a need to adjust your position on the bike as pedalling with arch of your foot will bring you forward slightly.
There is at least one other question on this forum that relates to this topic: Why not place the cleats further back on the foot?
I've added some of the information contributed by others here (as well as some more of my own thoughts/interpretation) that I think is relevant:
- There is an increased risk of your toe colliding with the front wheel. However, this is only really an issue when turning at low speeds.
- A mid-foot cleat/pedal position may be more suited to steady-state events (TT, Triathlon, etc), rather than for sprinting or criteriums where rapid changes of pace occur. Not sure whether there is scientific reasoning to support this, or if it is just some riders' preference.
- Moving your cleat in this manner (or any other significant change to your ride mechanics, for that matter) is likely to require time for your muscles to adapt to the new position. Incremental changes are likely to reduce the risk of injury associated with changing your ride mechanics.