According to the following Sinsy tutorial, if you put a hyphen as the lyric in the note following the one you want to slur, you should achieve what you want.

https://talcium.blogspot.com/2018/03/sinsy-english-tutorial.html

If you get a chance, you should try out Synth V by Dreamtronics. There are free trials you can download at the company's home page.

https://dreamtonics.com/synthesizerv/

Here is a song I put together as a male/female duet using Synth V.

★ a recent song of mine: Every Single Day (a duet using Synthesizer V’s vocaloids, Kevin & Natalie)


MY SONGS...
Audiophile BIAB 2025