This thread has a reference to some seeding.

Here is a link that might be useful: Heliopsis 'Midwest Dreams' vs. 'Summer Sun'

Heliopsis is a clumper. Summer Sun is a seed strain too. It is not homogeneous as far as the shape of flowers and colour are concerned. Each plant has its own shape of flowers(pointed or round petals and everything in between), from semi-double to fully double, from yellow to orange-yellow. Tough but not always totally self-supporting, so culling may be necessary. The main flower on the top of the stem is always bigger and fuller than the rest.

As mentioned above, it is a clumper. It does self-seed, but not as crazy much as some plants, and the seedlings are easy to either transplant where you want them, or just remove. So no worries!

Beth
Z5 northern MI

Excellent news! I don't mind a self sower. Sometimes your happy with more seedlings and it is convenient. Like little dividends. Anything that is easy to pull out and doesn't keep coming back on you, no matter how many times you pull it, is okay in my book. Thanks...