更改图例边框和图例标题之间的间距

Question

我正在尝试使用RStudio将图表保存为图元文件（* .emf）。除了图例的顶部边框和图例标题之间没有间隙之外，图表的格式在* .emf文件中看起来没问题。我该如何添加这样的差距？我使用的是基地R。

这是代码。我无法将* .emf文件上传到Stack Overflow。

cov       <- 1:20

B0.1      <-  0.2
B1.1      <-  0.2
B0.2      <- -0.2
B1.2      <-  0.1
B0.3      <- -0.6
B1.3      <- -0.02

y.1 <- exp(B0.1 + B1.1 * cov) / (1 + exp(B0.1 + B1.1 * cov))
y.2 <- exp(B0.2 + B1.2 * cov) / (1 + exp(B0.2 + B1.2 * cov))
y.3 <- exp(B0.3 + B1.3 * cov) / (1 + exp(B0.3 + B1.3 * cov))

par(mfrow=c(1,1), pty="s")

plot(cov, y.1, bty = "l", type = 'l', col = 'black', lwd = 2, lty = 1, 
     xlab = 'Cov', ylab = 'Probability', ylim=c(0,1))

     lines(cov, y.2, type = 'l', col = 'black', lwd = 2, lty = 2)
     lines(cov, y.3, type = 'l', col = 'black', lwd = 2, lty = 3)

     abline(v = 10, lwd = 2, lty = 6)

     title('My Plot')

     op <- par(cex = .67)

     legend("bottomright",          c('Prob 1', 'Prob 2', 'Prob 3'), 
                              col = c("black", "black", "black"), 
                              lty = c(1, 2, 3),
                              lwd = c(2, 2, 2),

                              y.intersp = c(1.5, 1.5, 1.5),

                              title = "Legend", cex = 1.00, text.width = 2.50)