I had that one over Norther Germany (whis is as flat as flat can be). Cloud streets with base at 1200 m and tops at 1800 m. Wave lift started just under the base in front (upwind) of the cloud, and I managed to go over the tops.
You need a wind shift of 30° or so at cloud base level, with the air becoming stable (and the convective layer to be significantly unstable so that the thermals are pushed far into the stable layer above).

Le jeudi 22 octobre 2020 Ã* 13:50:12 UTC+2, a écritÂ*:

John, the unusual pattern of what we called flatland wave has been experienced a few times here in Florida. In 1983 Bennie Flowers and myself flew at least two of these occurrences during a few weeks span. I was able to gather some good information on the weather conditions for one particular flight which included satellite photographs. Our late friend Harry Senn assisted in gathering and analyzing the information. On one particular flight Bennie and I rode this wave to about 25 miles offshore on the East Atlantic coastline, we could have easily made the Bimini. May1983, Soaring magazine, Catching A Florida Wave.
The lift started below the cloudbase and we flew between these strange lines or rows of clouds that looked like a long loaf of bread with about two or three miles between each cloud, as I recall the cloudbases were only about 3K AGL and we rode the wave to well over 10K AGL. Bob