How big was the eye of the El Reno tornado?
There is no eye in the centre of a tornado's funnel, if we see the eye as a near circular cloudless area from bottom to tropopause, surrounded by a wall of towering clouds. Some interpretational leeway may lie in the low angular windspeed in the centre of the vortex, but that is not comparable to a hurricane's eye. Force of the central updraft is still strong enough to keep debris in suspension.
A vortex forms from updraft, warm air including 'macroscopic particles' is sucked into the cloud, while a hurricane's eye forms because of sinking air in the centre of a much larger and longer lasting storm system. There may, though, be water spouts under the individual thunderstorms of a hurricane's eyewall. Cause for rotation of a hurricane is coriolis force, while the vortex rotation is thought to be caused by vertical windsheer in the horizontal inflow. Hurricanes gain their energy from warm sea water, while thunderstorms are caused by vertical labilization of the atmosphere along a frontal line.
Here's a publication about the El Reno tornado. No structure that could be interpreted as an eye can be found in the interpretation of the radar data (Figure 15), and there's still a huge black thundercloud right above it.
Thunderstorms with tornados and tropical storms like hurricanes and typhoons are fundamentally different in how they form and evolve, their size and structure, much information on both phenomena can be found on the internet.
And, btw., TS Marco 2008 didn't have an eye either, I believe.