It could just be a phase?? Jenna was a shocking 40min sleeper, and in the last month or so has slipped into these wonderful 90min sleeps. Ahhhh bliss!!
One thing I did read that has helped my sanity is maybe get the baby up after the 40mins, and let them play for 10-15 mins. Watch for the tired signs again (hard to miss this time... LOL) and then try to put them down again. This time I found I had to do a fair bit of rocking/patting, but she started to go down!!

When she woke up from the second 40min nap, she was the happy baby again. Just a suggestion - might not help, and might affect your night time sleeps, which just sound too lovely and I'm very jealous.

Walking in the pram with a daytime awake baby is good too - gets your mind off it!

Fi