That's right. You have to open from ACR "as a smart object" in order to be able to reopen that layer in ACR or create new smart object layers that will open in ACR.
As an alternative, check these Russell Brown scripts:
http://www.russellbrown.com/scripts_archive.html
Search the page for "Edit layers in ACR". There are a couple of scripts, depending on what version of Photoshop you're using.
Thanks for your reply and for the Russell Brown scripts link. I am on Photoshop CC, so not sure if the CS5/6 scripts would work.
In the meantime, I have found that if I import my tif file back into Lightroom, I can then choose
Edit in and
Open as a Smart Object in Photoshop. The previously modified tif, now as a smart object, can be made into a
new smart object via copy which can be edited in Camera Raw.