1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

t=int(input())
for _ in range(0,t):
    n=int(input())
    a=list(map(int,input().split()))
    b=set(a)
    b=list(b)
    if len(b)==1:
        print(-1)
    else:
        z=max(a)
        pp=-1
        p=0
        for i in range(0,len(a)):
            
            if a[i]==z:
                if i==0:
                    if a[i+1]<a[i]:
                        print(i+1)
                        p=1
                        break
                elif i==n-1:
                    if a[i-1]<a[i]:
                        print(i+1)
                        p=1
                        break
                elif a[i]>a[i-1] or a[i]>a[i+1]:
                    print(i+1)
                    p=1
                    break
        if p==0:
            print(pp)
