Hi Keen,

You said that a SLR was painful. A SLR test is a neural test which often/ever produces a tension over the sciatic nerve. But a nerve is a physical entity which has limited elastic properties.
But if you stretch lightly the sciatic nerve, you give a bit ROM to the nerve and reduce immediately pain. It is why you got quick improvement with dorsi-flexion.

Here is an visual explanation with a flash animation.
<a href="http://www.somasimple.com/flash_anims/nerves_ropes_02.swf" target="_new">http://www.somasimple.com/flash_anims/nerves_ropes_02.swf</a>

So, you may have no pain at heel when provoking lumbar spine but pain when doing a SLR where sciatic nerve is already near its limits.

Bernard, PT