Kovalainen told Finland's Turun Sanomat newspaper that the two outings late in 2013 have boosted his confidence, as he seeks a full-time return for 2014.
"Driving this (Lotus) car, a good car, I am now convinced that, with Caterham, I have developed as a driver in many areas compared to when I was at McLaren," he said.
Kovalainen's new race engineer Mark Slade, who has been working with Raikkonen full-time this year, agrees.
"Heikki is now more relaxed," said Slade, who worked with Kovalainen at McLaren. "He's been very good at adapting to the new car."
Kovalainen thinks he has done his quest to return to race action in 2014 no harm with his Lotus outings.
"I am on the right end of the timesheets, everyone can see that," the 32-year-old said.
"Now with a good car, I realise I am better than I was at McLaren," he is quoted by Germany's Auto Motor und Sport.
"I want to remain a formula one driver in all circumstances, even if it's only as a test driver."
Kovalainen has been strongly linked with a return for Caterham in 2014, but the latest rumours suggest rookie Marcus Ericsson could in fact line up alongside Giedo van der Garde.
Team boss Cyril Abiteboul confirmed in Brazil, however, that Caterham is still interested in Kovalainen.
"First of all I need to make sure that Lotus is not going to keep him," he smiled.