Stereo Spread not as wide??

I've been using Reaper on and off for years. When I decided to take audio engineering and mixing seriously I started with Pro Tools. I found it good... but it had a tendency to crash a lot, I didn't like that it wasn't very portable (for me this was very important as I did a lot of field and live recordings) and overall I didn't like the elitist feel to it. At the time I was broke and wasn't prepared to fork out hundreds for plugins, i just wanted to play around with free VSTs. I swithched back to Reaper and love it. It just makes more sense to me. However I have noticed that some of the recordings I did using Pro Tools tended to have a wider stereo spread than Reaper when listened to on headphones. Nothing really major and nothing any of my clients have said anything about but I couldn't help but notice it. I'm not going to switch back to Pro Tools as I've learnt how to do so much in Reaper now.

Has anyone else noticed this? is there a reason for it? is there a way I can achieve this without using a widener plugin? (which just sounds too artificial). Or could it be an audio quality thing when rendering/bouncing the finished track?

Stereo Spread not as wide??