Signature Spells and Heightened Spells

[Clonkeror]

So, I've been looking at possibilities for a level up and specifically Signature Spells for a Bard. Reading the feature, I thought it might be possible to take a Heightened Spell, say Grim Tendrils as a level 2 heightened, and take it as a level 2 signature spell, while taking a different one like Soothe, as a level 1 signature spell.

Hero Lab Online says it doesn't work that way, and yet in other places on the interwebs people are saying that is how it works, and I have found myself confuzzled.

Is there some place this point has been clarified to say one way or the other? Is the wording of the feature actually saying that if I have taken Grim Tendrils as a level 2 heightened, I can still pick it as my level 1 and cast it at any level?