Ltd exp trains - JR West Kansai Wide Area

I have read all the JR West Kansai Wide Area pass information that I can find and I have read that "ordinary car, reserved seating" on a limited express train requires a "separate express ticket".

I am confused as to what I would actually have to purchase ... Take this example:
On HyperDia, for a Limited Express Kuroshio 12 from Kiitanabe to Shin-Osaka on 10th July, the fare is:
Base fare: \ 3,020
Unreserved seat fee: \ 1,730
Reserved seat fee: Seat Fee:\ 2,250.

If I don't reserve a seat, I don't pay anything - is that correct?
If I do reserve a seat, do I pay \ 2,250, or \520 (the difference between \2,250 & \1,730)?

Thanks for clarifying this for me.

On HyperDia, for a Limited Express Kuroshio 12 from Kiitanabe to Shin-Osaka on 10th July, the fare is:
Base fare: \ 3,020
Unreserved seat fee: \ 1,730
Reserved seat fee: Seat Fee:\ 2,250.

It means that you have to pay 2250 yen if you use a reserved seat.

If I don't reserve a seat, I don't pay anything - is that correct?

That is correct.

If I do reserve a seat, do I pay \ 2,250, or \520 (the difference between \2,250 & \1,730)?

If you use a reserved seat, then only the base fare will be covered and you have to pay the limited express fee for a reserved seat (called "Reserved seat fee" by Hyperdia) which on July 10 is 2250 yen. Note that the fee various by +/- 200 yen depending on the travel date.

Thank you very much - that is much as what I thought, however I wanted to check that I had the correctly interpreted the meaning of "express ticket"